NEW DELHI -- When an acrid blanket of gray smog settled over India's capital last month, environmentalists warned of health hazards, India's Supreme Court promised action and state officials struggled to understand why the air had suddenly gone so bad.
The heavy smog has dissipated for the moment, but it has left behind a troubling reality for one of India's most important cities: Despite measures to improve air quality, pollution is steadily worsening here, without any simple solutions in sight.
"This is like a ding-dong battle," said Sheila Dikshit, the chief minister of the State of Delhi, moving her fingers like the flippers of a pinball machine. "We catch up with something; the pressures catch up more than that."
Delhi, a growing metropolis of nearly 20 million people, has struggled to reconcile its rapid economic growth with environmental safeguards. Over a decade ago, the city introduced a host of policies that raised emission standards, closed polluting industries and expanded green spaces. It made a costly investment to convert the city's buses and auto rickshaws to compressed natural gas. For a time, air quality visibly improved.
But those gains have been overwhelmed in recent years. "We have already plucked the low-hanging fruits, so to speak," said Anumita Roychowdhury, the executive director of the Center for Science and Environment here. "Now it's time for aggressive, second-generation reforms."
Ms. Roychowdhury and other environmentalists say the government must now concentrate on slowing the rising number of vehicles on New Delhi's roads. Each day, about 1,400 new vehicles hit the roads of the city, already home to over seven million registered vehicles, a 65 percent jump from 2003. As a result, fine-particle pollution has risen by 47 percent in the last decade. Nitrogen dioxide levels have increased by 57 percent.
Environmentalists recommend a hefty tax on diesel vehicles, a steep increase in parking charges and a rapid upgrade of the public transportation system to ensure more timely bus service and a better integration of buses and the metro rail system.
"These strategies can be implemented immediately and will have an immediate impact on the numbers of vehicles," Ms. Roychowdhury said. "We have to stop this untamed motorization now."
But government officials say that a mere crackdown on vehicles ignores other aspects of the problem. They note that New Delhi is landlocked and lacks the coastal breezes that flush polluted air out of other major Indian cities like Mumbai, Kolkata and Chennai. Ms. Dikshit said New Delhi's rapidly growing population and prosperity add to the pollution.
"It's an epicenter of trade, of commerce, of governance for this entire northern area," she said. As a consequence, Delhi "bears a much bigger burden."
Officials say much of the pollution comes from neighboring areas, where emissions standards are lower and environmental policies virtually nonexistent. For days after November's smog spell, many Delhi officials responded by blaming a coincidence of factors, including agricultural burnings in the neighboring states of Punjab and Haryana and the impact of a cyclone off the southern coast.
Weather conditions played a role, environmentalists agree, but that is no excuse for ignoring the underlying problems.
"The government cannot say that the smog was solely because of bad weather," said Mukesh Khare, a professor of environmental engineering at the Indian Institute of Technology in Delhi. "They are making excuses to avoid facing the fact that Delhi has a pollution problem once again."
Until two years ago, environmentalists and city officials in New Delhi lacked monitoring equipment to determine air pollution levels, and scientists and policy makers were dependent on ad hoc surveys conducted manually or on data from the national pollution body that often were incomplete or arrived too late.
In 2010, the Delhi government posted six state-of-the-art monitoring machines around the capital that now constantly measure a host of pollutants, sending real-time data to a publicly accessible Web site.
"We didn't really understand the situation before," said Mohan George, a scientist at the Delhi Pollution Control Committee. "Now we have authentic, continuous and reliable data."
In November, the machines recorded pollution levels at least six or seven times greater than the national standard for safe air. On Nov. 9, for instance, the levels of particulate matter called PM10 near the University of Delhi measured 908 micrograms per cubic meter, against the standard limit of 100, falling into the "very unhealthy" category.
The city's doctors are worried. Dr. Randeep Guleria, who runs the pulmonary medicine department at the All India Institute of Medical Sciences, said the number of emergency visits relating to respiratory and heart problems had risen sharply this winter.
What is going on in New Delhi reflects a larger trend. A recent study published in the medical journal Lancet shows air pollution has become a major health risk in developing countries, contributing to about 3.2 million premature deaths worldwide. South Asian countries are particularly vulnerable, the study found.
The local government has commissioned a study to understand what exactly caused the smog, and is working on an "air action plan" that would expand the subway system, introduce a network of bike lanes and make the city's roadways more friendly to pedestrians.
The Supreme Court, which has played the role of environmental watchdog in Delhi for more than a decade, has recommended a more politically delicate measure: imposing an "environment compensation charge" of 25 percent on new diesel vehicles and requiring a much smaller fee for existing gasoline- and diesel-powered cars.
Ms. Dikshit, Delhi's chief minister, has agreed to consider such a "green tax" and welcomed other solutions, even as she denied that the city's pollution was reaching alarming levels.
"What is alarming is the impact that Delhi's prosperity and its comfortable living is having on attracting more and more people to come here," Ms. Dikshit said. "How much we will be able to sustain that impact of people coming and never going out is a big question."
This article originally appeared in The New York Times.